Lubrication system

Abstract

A lubrication system comprises a lubricant reservoir, a lubricant supply passage fluidly connecting the lubricant reservoir and a space requiring lubrication, and a lubricant supply pump. The supply pump includes a piston having a first piston head slidably received in a chamber in fluid communication with the lubricant reservoir and a second piston head slidably received in a pumping chamber. The pumping chamber is divided into a first and second cavities by the second piston head. The first cavity is between the first piston head and second piston head. The first and second cavities are placeable in fluid communication with pressure sources externally of the pumping chamber to provide a pressure differential between the first cavity and the second cavity, whereby the piston may move as a result of the pressure differential to cause the first piston head to dispense lubricant from the lubricant reservoir to the space.

The invention claimed is: 
     
       1. A lubrication system comprising:
 a lubricant reservoir; 
 a lubricant supply passage fluidly connecting the lubricant reservoir and a space requiring lubrication; and 
 a lubricant supply pump, the lubricant supply pump comprising:
 a piston having a first piston head slidably received in a chamber in fluid communication with the lubricant reservoir; and 
 a second piston head slidably received in a pumping chamber; 
 the pumping chamber being divided into a first cavity and a second cavity by the second piston head, the first cavity being arranged between the first piston head and the second piston head; 
 the first cavity and second cavity being placeable in fluid communication with one or more pressure sources externally of the pumping chamber so as to provide a pressure differential between the first cavity and the second cavity whereby, the piston may move as a result of the pressure differential so as to cause the first piston head to dispense lubricant from the lubricant reservoir to the space through the lubricant supply passage; 
 wherein the pressure differential between the first and second cavities is derived from a difference in ambient pressure at ground level and the ambient pressure at altitude. 
 
 
     
     
       2. The lubrication system as claimed in  claim 1 , comprising one or more valves for controlling admission of fluid into and venting of fluid from the first and second cavities to control the pressure differential. 
     
     
       3. The lubrication system as claimed in  claim 1 , wherein a first cavity non-return valve is provided in fluid communication with the first cavity, the first cavity non-return valve being configured to allow venting of fluid out from the first cavity as a pressure outside of the pumping chamber falls, but to prevent admission of fluid into the first cavity as a pressure outside of the pumping chamber rises, the second cavity being vented so as to permit fluid flow into and out of the second cavity as a pressure outside the pumping chamber rises or falls, thereby providing the requisite pressure differential. 
     
     
       4. The lubrication system as claimed in  claim 1 , wherein a second cavity non-return valve is provided in fluid communication with the second cavity, the second cavity non-return valve being configured to prevent venting of fluid from the second cavity as a pressure outside of the pumping chamber falls but to allow admission of fluid into the second cavity as the pressure outside of the pumping chamber rises, the first cavity being vented so as to permit fluid flow into and out of the first cavity as a pressure outside the pumping chamber rises or falls, thereby providing the requisite pressure differential. 
     
     
       5. The lubrication system as claimed in  claim 1 , wherein the first piston head has a smaller cross sectional area than that of the second piston head. 
     
     
       6. The lubrication system as claimed in  claim 1 , wherein the first piston head is slidably received within the lubricant reservoir. 
     
     
       7. A screw actuator comprising:
 a lubrication system as claimed in  claim 1 , 
 wherein the space to be lubricated is an interface between a screw and a nut. 
 
     
     
       8. An aircraft comprising:
 a lubrication system as claimed in  claim 1 . 
 
     
     
       9. A method of supplying lubricant to a space requiring lubrication, the method comprising:
 pumping lubricant from a lubricant reservoir into the space by means of a piston having a first piston head which is slidably received in a chamber in fluid communication with the lubricant reservoir and a second piston head slidably received in a pumping chamber, the second piston head dividing the pumping chamber into a first cavity and a second cavity, and 
 controlling the differential in pressure between the first cavity and the second cavity such that the piston will pump lubricant from the lubricant reservoir when the pressure in the second cavity exceeds the pressure in the first cavity; 
 wherein the space requiring lubrication is on an aircraft; and 
 wherein the differential in pressure is derived from one of a difference in ambient pressure at ground level and ambient pressure at altitude, the method comprising venting the first cavity or admitting fluid into the second cavity to provide the pressure differential, and a difference in static and total pressure on the aircraft. 
 
     
     
       10. The method as claimed in  claim 9 , comprising controlling the differential in pressure by at least one valve in fluid communication with the first cavity and/or the second cavity. 
     
     
       11. The method as claimed in  claim 9 , wherein the space to be lubricated space is an interface between a screw and a nut in an actuator. 
     
     
       12. A lubrication system comprising:
 a lubricant reservoir; 
 a lubricant supply passage fluidly connecting the lubricant reservoir and a space requiring lubrication; and 
 a lubricant supply pump, the lubricant supply pump comprising: 
 a piston having a first piston head slidably received in a chamber in fluid communication with the lubricant reservoir; and 
 a second piston head slidably received in a pumping chamber; 
 the pumping chamber being divided into a first cavity and a second cavity by the second piston head, the first cavity being arranged between the first piston head and the second piston head; 
 the first cavity and second cavity being placeable in fluid communication with one or more pressure sources externally of the pumping chamber so as to provide a pressure differential between the first cavity and the second cavity whereby, the piston may move as a result of the pressure differential so as to cause the first piston head to dispense lubricant from the lubricant reservoir to the space through the lubricant supply passage; 
 the pressure differential between the first and second cavities is derived from a difference in static and total pressure in the aircraft, the second cavity being fluidly connected to a source of total pressure and the first cavity being connected to a source of static pressure. 
 
     
     
       13. The lubrication system as claimed in  claim 12 , comprising one or more valves for controlling admission of fluid into and venting of fluid from the first and second cavities to control the pressure differential. 
     
     
       14. The lubrication system as claimed in  claim 12 , wherein a first cavity non-return valve is provided in fluid communication with the first cavity, the first cavity non-return valve being configured to allow venting of fluid out from the first cavity as a pressure outside of the pumping chamber falls, but to prevent admission of fluid into the first cavity as a pressure outside of the pumping chamber rises, the second cavity being vented so as to permit fluid flow into and out of the second cavity as a pressure outside the pumping chamber rises or falls, thereby providing the requisite pressure differential. 
     
     
       15. The lubrication system as claimed in  claim 12 , wherein a second cavity non-return valve is provided in fluid communication with the second cavity, the second cavity non-return valve being configured to prevent venting of fluid from the second cavity as a pressure outside of the pumping chamber falls but to allow admission of fluid into the second cavity as the pressure outside of the pumping chamber rises, the first cavity being vented so as to permit fluid flow into and out of the first cavity as a pressure outside the pumping chamber rises or falls, thereby providing the requisite pressure differential. 
     
     
       16. The lubrication system as claimed in  claim 12 , wherein the first piston head has a smaller cross sectional area than that of the second piston head.